1. Field of the Invention
The present invention relates to a safety valve device for compressed gas cylinders and, more particularly, to a stand-alone safety valve configured to be seated in the port of a compressed gas cylinder, below and independent of the conventional primary gas valve, for the purpose of instantly shutting off gas flow in the event of mechanical deflection or severance of the primary gas valve, or on command.
2. Description of the Related Art
Compressed gas cylinders are potentially lethal missiles if the primary gas valve is severed or deflected so as to allow an uncontrolled release of the stored gas. Destruction from a runaway gas cylinder can be catastrophic in terms of human injury and property damage. An even more deadly potential exists if the cylinder contains toxic or explosive gases. Loss of life can result if these gases are accidentally released, whether or not the cylinder becomes an uncontrolled missile.
Primary gas valves have been designed so as to incorporate a safety shutoff device as part of a primary gas valve. In such devices, a secondary valve is incorporated into the primary valve, and it is biased into a held open position. At such time as the primary valve is severed, the secondary valve is actuated, preventing the sudden escape of gas from the high-pressure cylinder. Examples of prior art combination safety and service valves are shown and described in U.S. Pat. Nos. 3,648,893, 4,077,422, and 4,562,852. The secondary valves described in these patents include either a cylindrical plug which engages a flat seating surface, or a ball which engages a ball chamber, to close the flow passage.
The safety valve described in U.S. Pat. No. 4,907,617, authored by one of the inventors of the present invention, and having a common assignee, provided another means by which a safety valve could be integrated into a conventional primary valve. The safety valve portion of the primary valve includes a poppet seat and a poppet held off the poppet seat by a frangible element, which is held in compression by means of a helical spring. A severing of the primary valve, or other structural disruption of the valve, serves to break the frangible element, thereby seating the poppet in the poppet seat and shutting off the flow of gas from the cylinder. A unique advantageous feature of this safety valve is the use of a frangible element to hold off the seating of the poppet. This is not to say, however, that improvement of this earlier safety valve is not possible and indeed the present invention constitutes an improvement of the basic structure and characteristics of the safety valve described in the above-identified patent.
More particularly, while the earlier safety valve included a frangible element, the element will not break until the primary valve receives a significant blow resulting in the severing, or major structural distortion, of the primary valve. Therefore, it is desirable to provide a safety valve which shuts off gas flow upon relatively small deflections of the primary gas valve, or to shut off gas flow upon the command of the operator in the event the primary gas valve has become inoperative or ineffective due to leakage around the threads.
Further, the earlier safety valve must be mechanically integrated into the body of a primary gas valve. The retrofitting of a primary gas valve is difficult to perform and is met with disfavor by the manufacturers of primary valves. Therefore, it is desirable to provide a safety valve which could work cooperatively with conventional primary gas valves, but which does not have to be mechanically integrated into or require modification of the primary valve.
Even further, the earlier safety valve does not address the problem of gas leakage past the threads of the primary valve where the primary valve receives a blow resulting in damage to its threads. Blows to primary valves often result in leakage of gas about the threads, which can be extremely dangerous in the case of cylinders containing toxic or explosive gases. Therefore, it is desirable to provide a safety valve which forms an independent threaded seal with the cylinder, which will not be damaged in the event that the primary valve experiences thread damage.